In recent years, a fuel cell system has been suggested in which a variable gas supply device such as a mechanical variable regulator or an injector is provided in a fuel supply path for allowing a fuel gas (e.g., a hydrogen gas) supplied from a fuel supply source such as a fuel tank to flow into a fuel cell, whereby the supply pressure of the fuel gas from the fuel supply source can be changed in accordance with the operation state of the system (e.g., see Japanese Patent Application Laid-Open No. 2005-302571).